I have created database with 11.2.0.3 in RHEL 5. I have catalog database(RMAN) with version 10.2.0.1 and 5 databases with different versions(10.2.0.1,10.2.0.3,10.2.0.5) registered with this catalog databases.

Now I want to register the 11.2.0.3 database with catalog (RMAN) database.

The 11g database can be registered in a Catalog database that is 10.2.0.3 or higher (not 10.2.0.1). Also, the Catalog Schema should be an 11.2 or higher schema (meaning that you have to create a separate catalog schema for your 11.2 database when running the rman client from the 11.2 ORACLE_HOME).

When running an 11.2 rman client for an 11.2 target database, the catalog schema must also be 11.2 . So you will have to create a new catalog in the 10.2.0.3 database.
I would rather suggest an 11.2 database to hold the 11.2 catalog schema.

I have upgraded catalog databases to 10.2.0.3 and Now am able to use this catalog for all databases(10.2.0.1,10.2.0.3,10.2.0.5 and 11.2.03). Can I go like this as I don't want to create more databases for catalog.

A database can hold more than one catalog, each in a different database account. The catalog is created by the RMAN command "CREATE CATALOG" -- so it is created by the rman client that connects to the database.